Coating of fibrous or particulate inorganic or organic materials with activated carbon may be desirable for various applications such as reinforcement of matrices, or in some cases where a bed of these particles is used, to remove particulate and dissolved organics from a flow stream in a fluidized bed or packed bed. Particularly, such particles can be useful for water purification where particulate matter as well as organics have to be removed. Such activated carbon beads can also be useful in many pollution control applications where a hydrocarbon (VOC) is to be removed from air with particle beds of such material. The beads can be made of carbon alone without a filler, to obtain purely carbon beads.
Coating of particulates with carbon may be carried out by vapor deposition but this process is too expensive for most applications. Another way to carry out the coating is to coat the particles with a carbon precursor such as a thermosetting resin which is then cured, carbonized, and which can then be activated depending on the application. The obvious method to coat the particles would be to dip the particles in the resin and then try to separate the particles by spray drying or other conventional methods. This cannot be done however, because the resins do not cure till reaction is carried out at about 150.degree. C. for a period of time of about 2 hours. Before cure, the resin remains sticky and the coated particles cannot be separated. A large agglomerated mass is thus obtained. The only way to separate the particles is to grind the mass to a fine particle size. Although this can be done, it is difficult and expensive. Using resins such as phenolic novolaks which are solid powders at room temperature also does not work very well because the fine powders melt and go through a liquid phase at about 80-90.degree. C. at which point they stick together and form a big lump of material which cures at about 125-150.degree. C. Again the grinding and powdering of such a mass is difficult and expensive.
Any of the typical coating processes such as spray drying or fluidized bed coating do not work. The particles agglomerate and lose the free-flowing characteristic. Such agglomerated carbon particles cannot be activated properly, which is important for many applications. The problem of coating becomes more acute with fibrous materials because such materials have a natural tendency to agglomerate due to the inherent high aspect ratio. In addition to the fundamental problem of agglomeration, processes such as spray drying may be too expensive for certain applications.
It is desirable to be able to produce free-flowing activated carbon beads by a simple inexpensive method. The present invention provides such a method.